This inflammation is called pulpitis, and it can happen for various reasons. Occasionally, placing a restoration close to the pulp can cause it to become inflamed. Other times, the pulp may become inflamed due to an injury. In both of these cases, the pulp may calm down on its own, but sometimes it can die or become infected. The pulp can also become infected when tooth decay allows bacteria into the pulp. Sometimes there is no apparent reason.
When the pulp of a tooth becomes infected or dies, root canal therapy is necessary to save the tooth. The pulp is a soft tissue made up of nerves and blood vessels.